Re: [PATCH] libxtables: Dont initialize global xt_params

[Thomas Jarosch <thomas.jarosch@intra2net.com>]

On Thursday, 12. February 2009 16:14:23 Jan Engelhardt wrote:
> >1. Other people which don't know this "trick" will think
> >the variable is not initialized -> Hard to read.
>
> Well, maybe then they should get a better C book --
> automatic initialization is said to be(*) part of the C standard.
> And one should know the standard of a language IMHO.
>
> (*) Because it is not free, it remains a saga from people who do
> have access to it. :p

That is completly true. OTOH avoid the dark corners of the language.

> >2. If that variable gets moved f.e. inside a function, it will become
> >uninitialized. Also I'm not sure if the savings are even measurable...
>
> It seems to be for the Linux kernel. Especially when you happen
> to have large globals (both a lot of them, and large; e.g.
> foo[NR_CUPS]) this becomes a concern.

Well, I guess that's a job for the compiler/optimizer. I did a quick test by 
writing two versions of a small program initializing a static variable with 
zero and one version that doesn't (=zeroed in .bss). Guess what,
the size of the resulting executable stays the same.

When I initialize the variable with a non-zero value, then the program size 
increases. I tested "-O2", "-O0" and "-Os" and the results where the same.
Feel free to look at the assembler output, though I guess this optimization
is not measurable and makes the code harder to read :o)

Thomas